U.S. Pat. No. 4,057,204 issued Nov. 8, 1977 in the name of R. E. Zajac to Windings, Inc. ("Zajac") discloses a payout tube of the above described sort in which an annular flange encircles the tube near its exit end to provide a planar stop surface extending continuously around the tube and the tube has at such end, outward of the flange, on diametrically opposite sides of the tube, a pair of projections which extend radially out from the tube to lie over the flange and which are shown as being of triangular cross section in planes normal to the radial center lines of the projections. The walls of such projections towards that flange are planar and slope in opposite directions as seen in a direction along the tube diameter between those center-lines.
The Zajac tube is secured in position within the container by (a) providing in a wall of the container a circular hole of the tube's diameter and having equangularly spaced around it a pair of notches formed in the hole's circumference for receiving the tube projections, (b) positioning the tube inside the container to pass a stub portion of such tube through such hole and such projections from inside to outside through such notches until the tube flange bears against such wall around the circumferential margin of the hole, and (c) then turning the tube 90.degree. to cause portions of the wall around the tube to be interposed between such flange and the tube projections to thereby secure the tube to the wall. According to the Zajac patent as it is understood, what happens in the course of such turning is that, because the space between the flanges and the axially inner edges of the sloping projection walls towards the flange is a space less then the wall thickness of the container, the turning of the tube causes the inclined lower surfaces of the projections to ride up on the box material and grip into it to prevent accidental turning of the tube to an improper position. The Zajac patent also indicates in its abstract that improper turning of the tube is avoided because the effect of the tube projections on the box material is that the projections "dig into it".
The Zajac tube has features which may lead to the following disadvantages. First, the digging into the box material by the sharp inner edges of the tube projections may macerate the box material or otherwise weaken it so that it will no longer provide sufficient support to anchor the tube to the box. Second, the sharp leading outer edges of the triangular cross sections of the Zajac projections tend, at the beginning of turning of the tube, to dig into the box material and damage it and prevent further turning of the tube.